1. Field of the Invention
The present invention relates to a method and device for detecting and eliminating short-circuits in an electrolytic tank in which anode plates and cathode sheets have been immersed in a row alternately, close to each other, and wherein the total current of a cathode is determined by observing the magnetic field, temperature, or some other suitable quantity produced by the current of the cathode bar attached to the cathode sheet and being in contact with a conductor rail of the tank, in order to detect a possible short-circuit condition.
Although the invention can be applied in connection with any metal electrolysis, the description below relates to its application to copper electrolysis.
2. Description of the Prior Art
The electrolytic refining of copper is known to be performed as follows: crude copper anodes and cathode sheets, which serve as starting sheets on both sides of which pure copper will deposit, have been immersed alternately in rows in a flowing electrolyte, which can be a copper sulfate solution containing sulfuric acid. The anodes and the cathodes rest on conductor rails, the anodes supported by their lugs and the cathodes by transversal cathode bars from which the sheets have been suspended.
In order to produce effective precipitation and to save power consumption the anodes and cathodes must be rather close to each other, and, furthermore, the copper deposit may grow exceptionally rapidly at some points, and therefore short-circuit conditions are often created between the anodes and the cathodes in the tank. Another natural reason for this is that the starting sheets in particular curve easily, or a sheet may not be positioned properly halfway between adjacent plates.
Short-circuit condition here denotes a state deviating from the normal, in which case the total current of a cathode surpasses a certain, predetermined limit value. Naturally, if a short-circuit is created through, for example, a "bridge" growing between the anodes and the cathodes, the strength of the current increases gradually until it produces a strong short-circuit, and the change in the condition is thus not sudden.
The following methods are known for finding short circuits:
a. measuring of the voltage of an individual cathode bar over a predetermined length PA0 b. magnetic measuring of an individual cathode bar by means of a gaussmeter PA0 c. measuring of the temperature by means of an infrared camera and reading the temperature map of the tank.
Thus, these methods are based on the fact that an exceptionally strong current causes respectively (a) a greater voltage loss per length unit of the bar, (b) a stronger magnetic field around the bar, and (c) a higher temperature in the bar.
All these measuring methods are, however, capable of only locating the defective cathodes, which is only one-fifth of the work caused by short-circuits. Marking and repairing the defect have been manual so far.
For example, when using a gaussmeter the work has been performed as follows: the person performing the measuring walks along the cathode row and tests the current of each cathode bar by means of the gaussmeter measuring head. The meter has preferably a "red area" which indicates a field stronger than normal, i.e., a short-circuit condition. If one appears, the location of the cathode is marked by, for example, chalk or a piece of tape, and the sheet is repaired shortly after the measuring.
The repairing may be performed by simply moving the sheet; usually it is, however, necessary to lift the sheet up, remove the short-circuit bridges (protuberances) and straighten the sheet. Since a cathode weighs approx. 20-100 kg, depending on how far the depositing has progressed, the repair work is cumbersome and requires two persons. In addition, the walking on top of the tank during the measuring and repairing may cause new short-circuits.
Another known method is to lift all the cathodes from the tank after a couple of days' electrolysis, to straighten them in a press, and to reimmerse them in the electrolyte. In this case it is possible to keep the sheet straight since the metal deposits on their both sides increase their stiffness. Naturally, however, such an operation requires high-capacity lifting devices and presses, and a great deal of wasted work is performed since during the growth period of the cathodes (7-14 days) only a few percent of the sheets are short-circuited.